Continuously variable transmissions (CVT) include essentially two conical wheel pairs and a belt part designed, for example, as a thrust member belt. One of the conical wheel pairs is connected to a drive, for example, an internal combustion engine, while the other conical wheel pair is connected to an output. The drive conical wheel pair and the output conical wheel pair each generally comprise an axial fixed conical wheel and an axial movable conical wheel in order to adjust the ratio of the CVT transmission and the tension of the belt part. The drive conical wheel pair is also characterized as a drive disc or primary disc. The output conical wheel pair is characterized also as an output disc or secondary disc. The contact force of the axially movable conical wheels against the belt part takes place, in general, by the build up of hydraulic pressure, for example, via a pump. With a suitable selection of the distances or the contacting pressures of the conical wheels, the desired ratio of the CVT transmission and the required tension of the belt part can be adjusted. The pump for the hydraulic drive of the conical wheels can, for example, be driven by the internal combustion engine. For the force transmission from the internal combustion engine to the drive conical wheel pair, for example, a torque converter and a planetary set can be provided with clutches for forward travel and rearward travel.
The pull force, which is generated by the drive wheels of a motor vehicle, is determined by the torque at the transmission output (output torque) or by the transmission output power. The output torque is essentially dependent upon the two variables “transmission ratio” and “motor torque”. In a vehicle, which is equipped with a continuously variable transmission, an output torque, which is defined on the basis of the pull force command of the driver, can be practically realized by any desired number of combinations of motor torque and transmission ratio. In order to determine the particular combination of motor torque and transmission ratio suitable in the instantaneous driving situation, it has already been suggested to provide a characteristic field or a computation sequence so that a desired value for the transmission ratio can be determined as a function of the output rpm and the position of the accelerator pedal or of the desired value for the transmission output torque in accordance with pregiven operating strategies. The desired value for the motor torque is then determined in dependence upon the determined transmission ratio.